I don't know. The discussion Penny had with Charlie doesn't necessarily mean Naomi was lying.

Penny sends a transmission to the Looking Glass, could be for other reasons other than rescuing Desmond. Finds out she's speaking to Charlie. Penny is trying to figure out who Charlie is and where he is. Charlie brings up whether Penny is on a boat, which she's isn't.....so she doesn't know WTF Charlie's talking about. Charlie brings up Naomi the Parachutist. Penny doesn't know who Naomi is. It could be plausible Penny just doesn't know WTF Charlie is talking about, I would assume there's many people on the Boat....why would Penny know each one of their names......let alone their first name. It could be possible she just hasn't made the connection....."Oh you mean that boat". How many times has somebody you've met a few times comes up to you and you don't remember who they are right away. Or somebody references somebody else you know, and you say "Mike who? I don't know Mike" then you think a bit and it clicks "Oh you mean Mike from High school!"

But I guess you can say for the purposes of the show, we can assumes that Penny would know instantly what Charlie was talking about (As how she instantly knew Charlie was referring to her Desmond).....so since she didn't know Naomi, it shows that Naomi wasn't working for Penny.

Well even if that's the case......it would appear that Naomi did get the Losties off the Island with the Sat Phone, even though she died in the process. Whoever she was working for somehow eventually picked up the Losties and got them back to civilization relatively unharmed. So Naomi did in fact help the Losties, dispite possible lying about who she worked for. If I was a Lostie that wanted to be rescued from the Island, and she made it happen, I would say Naomi was trustworthy and wasn't lying.